Human colostrum is an important source of protective, nutritional and developmental factors for the newborn. We have investigated the low abundance proteins in the aqueous phase of human colostrum, after depletion of the major proteins secretory IgA, lactoferrin, alpha-lactalbumin and HSA by immunoabsorption, using 2-D LC and gel-based proteomic methods. One hundred and fifty-one proteins were identified, 83 of which have not been previously reported in human colostrum, or milk. This is the first comprehensive proteomic analysis of human colostrum produced during the first 48 h of lactation. © 2006 Wiley-VCH Verlag GmbH & Co. KGaA.